1. Field of the Invention
The present invention is directed to a nuclear magnetic resonance tomography apparatus of the type operable using a pulse sequence according to the echo-planar imaging method.
2. Description of the Prior Art
In the known echo-planar imaging method, a read-out gradient is employed which consists of a number of sub-pulses of alternating polarity and at least one phase-coding gradient are simultaneously generated after a radio frequency excitation pulse per data acquisition. The arising signals are digitized and are entered into a row of a raw data matrix in the k-space for each sub-pulse of the read-out gradient. The rows are ordered according to the phase factors defined by the phase-coding gradient. A sequence of this type according to the echo-planar method is described in European Application 0.076 054. Although extremely short image registration times (30 through 100 ms) can be achieved with this known EPI method, the image resolution in the phase-coding direction is limited by the limited number of achievable echoes, and is limited in read-out direction by the area under the sub-pulses of the read-out gradient, which cannot be arbitrarily increased. In conventional EPI methods, a 128.times.128 raw data matrix is typically employed.